Question

I have a strong spring attached to a wall that has a spring constant of 700 Newtons per meter. Our trusty assistant Ed pulls on the spring and stretches it a distance of 20 centimeters. You then take over from that point and pull to stretch the spring 10 more centimeters so that it is stretched 30 centimeters total from the beginning. Calculate the work done by Ed and the work done by you in this process. At time t = 0 seconds you throw a ball sideways at a speed of 19 meters/second towards a wall that is 6 meters away from you. If the ball bounces off the wall elastically with the same 19 m/s sideways speed, at what time will the ball get back to you? If sound travels at a speed of 345 meters per second, how much time does it take sound to travel 5 miles? (1 mile = 1609 meters)

Answer 1

1. k = 700 N/m

Work done by Ed = 700 x 0.20^2 /2 = 14 J

Work done by you = 700 (0.30^2 - 0.20^2) / 2

= 17.5 J

2. total distance = 6 + 6 = 12 m

t= d /v = 12 / 19 = 0.63 sec

3. t = (5 x 1609 m) / 345 m/s

t = 23.3 sec